The present invention relates to SCUBA diving gauges.
SCUBA diving gauges provide necessary information to a SCUBA diver under water. A pressure gauge is typically coupled by a hose to the SCUBA tank to provide the diver with an indication of the pressure of the air in the tank. Additional gauges may provide information regarding water depth or elapsed time on a dive. Some gauges are analog with a pointer on a display indicating the value. Other displays provide a digital readout which provides greater accuracy but is more difficult to relate to a maximum value at a quick glance.
The various gauges use transducers to measure the particular parameter being monitored. For instance, a pressure transducer is coupled to a hose to the SCUBA tank to provide a pressure signal. This is a differential signal which then has to be amplified to be analyzed. Because of the limited size of a gauge and the need for low power consumption, it is desirable to construct the circuitry in CMOS (complimentary metal oxide silicon). Unfortunately, it is difficult to design circuitry in CMOS to do such amplification.
The simple provision of air pressure in a SCUBA tank in water depth enables a diver to calculate other parameters which he needs to know when he is diving. For instance, the amount of time a diver can stay under the water for a given amount of air pressure in the tank becomes shorter as the water depth increases. This is because his lungs require air under higher pressure to balance the higher outside water pressure. It would be desirable to have a gauge which would eliminate the need for the diver to do this mental calculation. The amount of time is further affected by the breathing rate of the diver, with a faster breathing rate obviously reducing the amount of air in the tank at a quicker rate.
In addition, nitrogen in the air inhaled by a diver builds up in the tissues of his body, and upon ascent to the surface, this nitrogen will expand inside his tissues. If the nitrogen level is above a certain amount, the diver will experience what is commonly referred to as the "bends." Accordingly, a diver needs to know the amount of time he can stay under water without experiencing the bends. This amount of time is shorter at greater depths because more nitrogen at high pressure is forced into his body. This time can be calculated using tables produced by the U.S. Navy by looking up the amount of time spent at each depth. In the event the diver has stayed down too long, he must make stops at certain shallow depths during his ascent to allow the nitrogen to gradually ease its way out of his tissues. The depth of these stops and the amount of time required at each can be again determined from such U.S. Navy tables.
It can be seen that there is a need for a diving gauge providing the above described information to a diver in an easily readable form. A diver under water will normally be occupied with salvage work, spear fishing, etc. and will not want to take the time to figure out a complicated display or make calculations from such a display.